Apparatus line for manufacturing seamless steel pipe and tube and method of manufacturing duplex seamless stainless steel pipe

Abstract

An apparatus line for manufacturing seamless steel pipes and tubes includes: a heating apparatus for heating a steel raw material; a piercing apparatus for piercing the heated steel raw material thus forming a hollow material; and a rolling apparatus for applying working to the hollow material to form a seamless steel pipe having a predetermined shape. A cooling apparatus is arranged on an exit side of the rolling apparatus. A heated steel raw material is worked by the rolling apparatus after being pierced by the piercing apparatus, and thereafter, using a surface temperature of a hollow piece before being cooled by the cooling apparatus as a cooling start temperature, the hollow piece is cooled to a cooling stop temperature differing by 50° C. or more from the cooling start temperature and being equal to or above 600° C. at an average cooling speed of 1.0° C./s or more in terms of an outer surface temperature.

What is claimed: 
     
       1. An apparatus line for manufacturing seamless steel pipes and tubes comprising:
 a heating apparatus for heating a steel raw material; 
 a piercing apparatus for piercing the heated steel raw material to form a hollow material; 
 a rolling apparatus for applying hot working to the hollow material to form a seamless steel pipe having a predetermined size; 
 a cooling apparatus arranged on an exit side of the rolling apparatus; and 
 a heat-retention apparatus having a heating function arranged directly following an exit side of the cooling apparatus, the heat-retention apparatus having a heating capability where an average heating speed at a position on an outer surface of a material to be heated is set to 1.0° C./s or more in heating, the heat-retention apparatus further having a heat-retention capability where an average cooling speed at a position on an outer surface of a material to be cooled is set to 1.0° C./s or less. 
 
     
     
       2. The apparatus line for manufacturing seamless steel pipes and tubes according to  claim 1 , wherein
 the cooling apparatus has a cooling capability where an average cooling speed at a position on an outer surface of a material to be cooled is set to 1.0° C./s or more.